The most senior U.S. diplomat for Asia has arrived in the Philippines and will meet the country's foreign minister on Monday amid confusion over the status of ties between the two long-time allies, said the U.S. embassy in Manila.

The visit by U.S. Assistant Secretary of State for East Asian and Pacific Affair Daniel Russel is part of a three-nation swing through Southeast Asia that also includes Thailand and Cambodia, the U.S. State Department announced on its website.

Russel arrives as confusion lingers over Manila's ties with Washington, with President Rodrigo Duterte saying on Saturday the United States remains the Philippine's "closest friend", after earlier provoking alarm by announcing his country's "separation" from the United States and realignment with China.

The United States is one of the Philippine's largest trading partners and its closest security ally for about ۷۰ years.